Array antennas, such as passive flat plate array antennas, that can provide larger gain and wider bandwidths are in continuous demand for various satellite and point to point communications applications. In a majority of these antennas, the radiating antenna elements are fed by series of corporate feed structures within a corporate feed network that begins with one or two inputs, joined/combined via a (reactive) 3-port T structure. Additional 3-port T structures making up the larger corporate feed network are the main contributors to the amplitude and phase distributions of the radiating elements. These T structures are designed and constructed to provide “widest band” and appropriate power division at each level before ending in the radiating antenna element. To obtain larger gain and bandwidth, it is imperative that each component of the corporate feed network (e.g., each 3-port T structure) and the radiating antenna elements be designed with the lowest possible reflection and the widest bandwidth performance.
However, obtaining a very low reflection (<−40 dB) by each component becomes exceedingly difficult due to the geometry and the manufacturing tolerances associated with today's array antennas. This in turn makes it difficult to achieve very low input reflection coefficient for the entire array. Powerful 3D simulation software has been used to optimize the design and the construction of the feed components. But, the inherent performance limitation of each component set by its boundary conditions, geometrical configuration, and the realistic achievable dimensional tolerances limit the optimized enhancements.
The addition of tuning circuitry to the antenna array input has also been tried to minimize the entire reflection. Unfortunately, the tuning circuitry typically cannot provide the required “wideband” performance if the amplitude of the reflection is large (>−8 dB) and/or highly oscillatory. Furthermore, the tuning circuitry does not provide any benefit with respect to the reflections which occur closer to the radiating antenna elements, hence affecting the radiation pattern.
In view of the aforementioned shortcomings, there is a strong need in the art for an array antenna in which the total input reflection coefficient of the array antenna may be lowered to an acceptable level over wider bandwidth, without reliance on tuning circuitry at the input and without significant degradation of the input reflection or the radiation pattern.